1. Field of the Invention
This invention relates, in general, to retractable safety belts in vehicles, and in particular, to an apparatus for locking the safety belts against further extension during emergency conditions, such as a forceful collision of the vehicle.
2. Summary of the Prior Art
Safety belts have come to be widely employed in the vehicles manufactured in this country within the last decade. These belts usually include at least a waist belt, and may also incorporate one or more belts passing across the chest of the wearer. Typically, the belts are retractably-retained within the vehicle by spring-wound reels attached to the structure of the vehicle which retain the belts in the retracted position until extended by the wearer across the wearer's body to mate with a belt retaining device, such as a quick-release buckle.
Devices have been developed heretofore for use in automotive vehicles for locking the safety belts by means of inertia sensors used in conjunction with the retractor reel which automatically lock the retractor reel against further extension of the belt in the event of an emergency, such as the sudden acceleration or deceleration of the vehicle. In testing such systems, it was found that, upon the locking of the reel itself, a certain amount of extension of the safety belt can still occur, depending upon the manner in which the belt is wound about the reel and the inertial force incident upon the belt as a result of the weight of the wearer's body. Thus, for heavier individuals, subject to forceful accelerations or decelerations, the belt has a tendency to "spool" and compress itself upon the reel, which permits an undesirable further movement of the belt in the extensive direction. As a consequence, locking devices have been developed which incorporate a belt-clamping device in addition to the inertially-locked reel for preventing the continued extension of the belt following lockup of the reel. Two such devices are disclosed in U.S. Pat. No. 4,451,062 to Ziv and U.S. Pat. No. 4,492,343 to Ziv, et al., and both assigned to the Assignee of the present invention.
In these prior art devices, the belt-clamping means comprises one or more clamping wedges slidably retained against one or more inclined-plane surfaces through which the belt passes. Movement of the wedges in the direction of further extension of the belt causes the wedges to move together to clamp the belt securely therebetween with a force which increases in proportion to the movement of the wedges in the extensive direction. In U.S. Pat. No. 4,451,062 above, the initial clamping movement of the wedge(s) is provided by a biasing means, comprising, in the two alternative exemplary embodiments, a resettable spring or an electrical solenoid. In U.S. Pat. No. 4,492,348, the biasing means for the clamping device comprises the inertially-locked retractor reel which is slidably-mounted for movement with respect to the clamping means such that, when the inertia reel is locked against further extensive movement of the belt, the reel is biased against the clamping means to cause the wedges to clamp the belt against further extensive movement.
In the first of these prior art references, the belt clamping means must be manually reset to release the belt from the clamped position. In the latter reference, although one of the embodiments disclosed resets automatically, it has been found that such inertia-reel-actuated clamps are sensitive to the amount of belt which is retracted onto the reel, i.e., the angular acceleration detected by the reel is different for the same inertial forces exerted upon the belt, depending upon the amount of belt material which is wound onto the reel.